Vulcanization accelerators for natural and synthetic rubber



Patented June 3, 1 947 VULCANIZATION ACCELERATORS FOR NATURAL AND SYNTHETIC RUBBER Elmer W. Cook, New York, N. Y., and Edwin 0. Hook, Norwalk, Conn, assignors to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Application March 23, 1944, Serial No. 527,826

6 Claims.

erators comprising reaction products of zinc chloride, formaldehyde, mercaptobenzothiazole and a monoarylguanidine.

The following examples, in Which parts are given by weight, are illustrative of suitable methods of producing these vulcanization accelerators.

Product A To a solution of 7 parts (1 mol) of zinc chloride in 10 parts water, 16.5 parts (1 mol) of monophenylguanidine carbonate Was added and the mixture heated to 105 C. for minutes to drive off carbon dioxide and water. A mixture of 50 parts (6 mols) of mercaptobenzothiazole and 9 parts (2 mols) of paraformaldehyde ((CH2O)3) wa added gradually to the melt which was maintained at 130-135 C. for about 35 minutes. On cooling, a hard, brittle, ambercolored resin was obtained which was readily ground to a fine powder.

Similarly, other accelerators may be prepared by varying the proportions. Typical compounds are those prepared by reacting mixtures containing the reactants in the following molar proportions, phenylguanidine carbonate: zinc chloride: formaldehyde: mercaptobenzothiazole=1:l:2:2,andl:l:8:8.

Product B Starting with a mixture of 7.5 parts hydroxyphenylguanidine (2 mols), 3.4 parts zinc chloride (1 mol), 415 parts paraformaldehyde (2 mols),'

Compounds Buna-S 100 100 100 Carbon Black 50 50 50 5 5 5 5 5 5 2 2 2 1. 5

1.1 Product B l 1 SET-UP TESTS-WILLIAMS 3 MIN. Y AT 100 INCHES No Heat .157 158 164 After 1.5 hours in boiling water 217 186 195 Change, per cent +38. 2 +17. 7 +18. 9

SHORE HARDNESS 260 165 500 250 1,935 1,900 Elongation; Ber cent 55 730 680 60 Cure at 141 Modulus at 200% 1 645 535 350 Modulus at 800% 1, 270 l, 065 735 Tensile 1 2, 665 2, 660 2, 125 I Elongation get cent L... 490 540 605 Cute at 141 A Modulus at 200% 1 760 665 520 Modulus at 300% 1, 610 l, 290 1,070 Tensile 1 2, 950 2, 665 2, 215 Elongation, per cent 470 480 490 1 Lb./sq. in. I Elongation at break.

In the set-up tests, the highest percentage change on heating for 2.5 hours in boiling water indicates the greatest set-up and tendency to scorch or precure. The products of the present invention show more delayed accelerator action than mercaptobenzothiazole but, at full produce comparably cured products, even using smaller amounts of the latter material, indicating that our products are stronger accelerators.

As will be seen from the above tests the compounds of the present invention have strong accelerator action. These accelerators do not bring about undue procure and give hard cured stocks. Similar results are obtained with natural rubber and the various synthetic rubber-like materials which may be vulcanized in the presence of sulfur. The proportion of accelerator used may be varied widely although, for most purposes, the least amount of accelerator is utilized which will give the desired results. Of course, mixtures of the rubber-like materials with each other or with natural rubber may be vulcanized with the accelerators of the present invention. The vulcanized compositions using these accelerators give somewhat lower rates of cut-growth than mercaptobenzothiazole and this property is very valuable, especially in synthetic rubber compositions.

The present invention is not restricted to the specific processes given for the production of the accelerators since the methods of manufacture may be varied considerably to obtain substantially the same results. In place of the monophenylguanidine specifically set forth, monoorthotolyl-, p-tolyl, xylyl, naphthyl, alkyl-oxyphenyl guanidines and similar monarylguanidines may be used.

We claim:

The process which comprises vulcanizing rubber and sulfur-vulcanizable rubber-like materials in the presence of sulfur and a powdered, resinous fusion product of approximately 1 mol of zinc chloride, 1 to 2 mols of a monoarylguanidine, 2 to 8 mols of paraformaldehyde and 2 to 8 mols of mercaptobenzothiazole.

2. The process which comprises vulcanizing rubber and sulfur-vulcanizable rubber-like materials in the presence of sulfur and a powdered, resinous fusion product of approximately 1 mol of zinc chloride, 1 to 2 mols of monophenylguanidine, 2 to 8 mols of paraformaldehyde and 2 to 8 mols of mercaptobenzothiazole.

3. A vulcanizable composition comprising sulfur, an unvulcanized material selected from the group consisting of rubber and sulfur-vulcanizable rubber-like materials, and a powdered, resinous fusion product of approximately 1 mol of zinc chloride, 1 to 2 mols of a monoarylguanidine, 2 to 8 mols of paraformaldehyde and 2 to 8 mols of mercaptobenzothiazole.

4. A vulcanizable composition comprising sul fur, an unvulcanized material selected from the group consisting of rubber and sulfur-vulcanizable rubber-like materials, and a powdered, resinous fusion product of approximately 1 mol of zinc chloride, 1 to 2 mols of monophenylguanidine, 2 to 8 mols of paraformaldehyde and 2 to 8 mols of mercaptobenzothiazole.

5. A composition comprising a material selected from the group consisting of rubber and sulfur-vulcanizable rubber-like materials, vulcanized in the presence of sulfur and a powdered, resinous fusion product of approximately 1 mol of zinc chloride, 1 to 2 mols of monoarylguanidine, 2 to 8 mols-of paraformaldehyde and 2 to 8 mols of mercaptobenzothiazole.

6. A composition comprising a material selected from the group consisting of rubber and sulfur-vulcanizable rubber-like materials, vulcanized, in the presence of sulfur and a reaction product of zinc chloride, monophenylguanidine, 2.to 8 mols of paraformaldehyde and 2 to 8 mols of mercaptobenzothiazole.

ELMER W. COOK. EDWIN O. HOOK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,173,731 Scott Sept., 19, 1939 2,269,472 Neal et al. Jan. 13, 1942 2,397,409 Davis Mar. 26, 1946 2,259,414 Davis Oct. 14, 1941 

